Linear motor having polygonal shaped coil units

ABSTRACT

The embodiments describe linear motor configurations having a polygonal shaped motor coil. The motor coil is e.g. hexagonal, diamond shaped, or double diamond shaped. Coil units are formed in a closed electrically conductive band surrounding a void. Coil units are formed e.g. from flex circuit material or by winding in a racetrack or folded tip fashion. Coil units are arranged in an overlapped shingle like manner to form a motor coil with substantially uniform thickness and high conductor density, providing high efficiency. Due to its substantially uniform thickness, the motor coil has a substantially flat cross section that allows the motor coil to be easily installed and removed from its associated linear magnetic track. The embodiments enable both moving coil and moving magnet linear motor configurations.

This application is a continuation of Application Ser. No. 09/059,056filed Apr. 10, 1998, now abandoned.

FIELD OF THE INVENTION

This invention relates to motors, and more specifically to highperformance linear motors.

BACKGROUND

Linear motors are commonly used, for example, in micro-lithographicinstruments for positioning objects such as stages, and in otherprecision motion devices. A linear motor uses electromagnetic force(normally called Lorentz force) to propel a moving part.

In FIG. 1A (reproduced from FIG. 1 of Itagaki et al. U.S. Pat. No.4,758,750, incorporated herein by reference in its entirety) aconventional linear motor includes magnets 2 which form one magnet pairand create a magnetic field in between. The magnetic poles N (north) andS (south) are shown. Similarly, the adjacent magnets form another magnetpair and create a magnetic field of opposite polarity. The width of twoadjacent magnets plus two spaces between the magnets defines themagnetic pitch PM of the motor. The magnetic flux direction across a gap4 is indicated by arrows 7 and 7 a. A moving coil unit 12 haselectrically conductive wires laid out in a direction perpendicular tothe plane of the figure. An electric current is passed through thewires, in a direction either into the plane of the figure or out of theplane of the figure.

As those skilled in the art will recognize, a wire carrying an electriccurrent in a magnetic field creates Lorentz force, the formula of whichis:

F=NLB×I

Where F represents Lorentz force, N the number of wires, B the magneticflux, and I the electric current. For a coil with a given length L andmagnetic flux B, to maximize force F, one has to maximize the number ofwires N and current I. The above formula determines both the magnitudeand the direction of force F, since force F, magnetic flux B, andcurrent I are all represented as vectors, and the symbol “×” representsvector cross product multiplication. As those skilled in the art willrecognize, a task in motor design is to maximize F/{square root over(P)}, or the “motor constant” where

F/{square root over (P)}=NLBI/({square root over (I²R+L )})= NLB/{squareroot over (R)}.

In the above expression, F is the scalar value of vector F, while P isthe amount of power consumed by the motor. For each particular designconfiguration, the motor constant is directly related to the “copperdensity,” which is defined as the total wire cross sectional area as apercentage of the entire coil cross section. (The coil wires are oftenmade of copper.)

In the configuration shown in FIG. 1A, the Lorentz force created by thecurrent in coil unit 12 causes the coil to move. While traveling in theright direction of FIG. 1A, coil unit 12 eventually leaves the field ofmagnets 2 and enters the field of the adjacent magnets. Since thissecond magnetic field has a reversed polarity relative to that of thefirst magnetic field, the current in coil unit 12 must reverse inpolarity so as to maintain the direction of Lorentz force. The reversalof the direction of the electric current is accomplished by acommutation circuit familiar in the art (not shown).

FIG. 1B, reproduced from FIG. 2 of Itagaki et al., is a cross-sectionalview of the conventional linear motor of FIG. 1A, viewed along the lineII—II in FIG. 1A. In such a linear motor at the coil head area 12′, thecoil heads are stacked on top of each other. This arrangement requires awide head area 12′.

Such a conventional linear motor has several disadvantages, one of thewhich is the difficulty of installation and removal. As shown in FIGS.1A, 1B, a magnetic track is formed by magnets 2 and the magnetic siderails 3. The magnetic track has a wide head area configured to match theshape and size of the wide head area 12′ of coil assembly 12. To removecoil assembly 12 from the magnetic track, coil assembly 12 must slideaway from the magnetic track in a direction perpendicular to the surfaceof the paper. Since the equipment (e.g. an X-Y stage) attached to coilassembly 12 is often heavy and difficult to handle, special tools aretypically required during installation and removal of coil assembly 12.

Another disadvantage of a conventional linear motor coil is its lowefficiency. FIG. 2 shows a cross sectional view of a linear motor coiltaken at a cross section perpendicular to the wire direction. Since thewire is not close packed, air gaps 50 inevitably result, substantiallylowering the conductor density of the coil. As discussed above, lowerconductor density often corresponds to lower motor efficiency.

It is therefore desirable to provide a linear motor having a motor coilwith improved efficiency, low heat dissipation, and easy installation.

SUMMARY

A motor in accordance with the invention overcomes the above and otherdrawbacks of conventional linear motors. According to the invention, alinear motor comprises a motor coil in cooperation with an associatedmagnetic track. The motor coil includes a linear assembly of coil units,each similar to the other. Each coil unit has an electrically conductivewire wound into a closed band in a predetermined number of layers,typically a single layer. The shape of the closed band is geometricpolygonal, such as diamond shaped, hexagonal, or double diamond shaped,having inner edges surrounding a void. Some embodiments comprise a rowof parallelogram shaped closed bands folded into a row of double diamondshaped coil units. In some embodiments, the width of the void is anintegral multiple of the width of the closed band.

The coil units are made e.g. of flex circuit material or by windingelectrically conductive wires in a racetrack or folded tip fashion. Insome embodiments the width of a coil unit is equal to the magnetic pitchof the associated magnetic track. In other embodiments the width of acoil unit is equal respectively to one-half or two-thirds of themagnetic pitch.

Advantageously this arrangement provides high electrical efficiency andease of disassembly. The coil units are stacked together in a partiallyoverlapped fashion to form a row of coil units in the motor coil so thatthe number of layers of wire in the useful area is substantially uniformacross the entire coil. Unlike the wide end coil shape of Itagaki etal., the present shape is more planar (not flared out at the end) and sohas a flat cross section that allows the coil to be easily removed fromand installed in the magnetic track.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a plan view of a conventional linear motor;

FIG. 1B is a cross-sectional view of the conventional linear motor ofFIG. 1A, viewed along the line II—II;

FIG. 2 is a cross-sectional view of a conventional motor coil units,showing inefficiently used cross-sectional area;

FIG. 3A is a plan view of a race track type diamond shaped coil unit,according to the invention;

FIG. 3B is a cross-sectional view of the tip area of the race track coilunit of FIG. 3A, according to the invention;

FIG. 3C is a view along line 3C-3C if FIG. 3B;

FIG. 4A is a perspective view of an apparatus for winding a race tracktype wire band, according to the invention;

FIG. 4B is a perspective view of a section of an apparatus for pressinga wire band into the final shape of a coil unit, according to theinvention;

FIG. 4C is a perspective view of a race track type coil unit, accordingto the invention;

FIGS. 5A and 5B are respectively a plan view and an end view of a racetrack type diamond shaped linear motor coil suitable for a fixedmagnetic track motor, according to the invention;

FIGS. 6A and 6B are respectively a plan view and an end view of adiamond shaped folded tip coil unit, according to the invention;

FIGS. 7A and 7B are respectively a plan view and an end view of a motorcoil suitable for a fixed magnetic track motor using diamond shapedfolded tip coil units, according to the invention;

FIG. 8A is a perspective view of an apparatus for winding a diamondshaped folded tip wire band, according to the invention;

FIG. 8B is a perspective view of an alternative apparatus for winding adiamond shaped folded tip wire band, according to the invention;

FIG. 8C is a perspective view and FIG. 8D is a side view of an apparatusfor pressing a folded tip wire band into the final shape of a motor coilunit, according to the invention;

FIG. 9A is an exploded plan view of a diamond shaped coil unit using aflex circuit, according to the invention;

FIG. 9B is a plan view of a linear motor coil using flex circuit diamondshaped coil units, according to the invention;

FIGS. 9C, 9D, and 9E are schematic plan views of linear motor sectionsusing diamond shaped coil units, showing the coil unit width relative tothe magnetic pitch, according to the invention;

FIG. 10A is a plan view of a hexagonal coil unit, according to theinvention;

FIGS. 10B and 10C are schematic plan views of a linear motor sectionusing hexagonal coil units, showing the coil unit width relative to themagnetic pitch, according to the invention;

FIGS. 11A, 11B, and 11C are respectively a plan view, a cross-sectionalview, and a perspective view of a folded tip hexagonal coil unit,according to the invention;

FIG. 12 is a perspective view of an apparatus for winding a folded tiphexagonal wire band, according to the invention;

FIGS. 13A and 13B are respectively a plan view and an end view of alinear motor coil suitable for a moving coil linear motor using foldedtip hexagonal coil units, according to the invention;

FIG. 14 is a partial plan view of a section of a linear motor coil usingtight wound folded tip hexagonal coil units, according to the invention;

FIG. 15 is a partial plan view of a linear motor coil using loose woundfolded tip hexagonal coil units, according to the invention;

FIG. 16A is a schematic plan view of a row of conductor legs formed on asheet of flex circuit, suitable for making hexagonal flex circuit coilunits;

FIG. 16B is a perspective view of a series of hexagonal coil unit legs,illustrating the spatial relationship and the electrical connectionamong the coil legs;

FIG. 16C is a cross-section view of a linear motor coil core made offlex circuit, illustrating the structure and the electrical connectionof the coil core;

FIG. 16D is a schematic plan view of a linear motor coil made of flexcircuit including several layers of coil units, illustrating theelectrical connection between different coil units;

FIG. 17A is a schematic diagram illustrating the formation of a racetrack double diamond shaped coil unit by folding a parallelogram shapedwire band, according to the invention;

FIG. 17B is a schematic diagram illustrating the formation of a foldedtip double diamond shaped coil unit by folding a parallelogram shapedwire band, according to the invention;

FIG. 18 is a plan view of stacked parallelogram shaped wire bands priorto folding to form a row of race track double diamond shaped coil units,according to the invention;

FIG. 19 is a plan view of a row of double diamond shaped coil unitsformed by folding the row of stacked parallelogram shaped wire bands ofFIG. 18, according to the invention;

FIG. 20A is a perspective view of a moving magnetic track according tothe invention;

FIG. 20B is a schematic plan view of the magnetic track of FIG. 20A,showing the magnetic flux path, according to the invention; and

FIG. 21 is a perspective view of a fixed magnetic track suitable for amoving coil linear motor, according to the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In accordance with the invention, a linear motor coil includes a linearassembly of coil units, each similar to the other. Each coil unit has anelectrical conductor formed into a closed band in a designated number oflayers, typically a single layer. The shape is that of a substantiallyplanar geometric polygon, such as diamond shaped, hexagonal,parallelogram, or double diamond shaped. The coil units are formed frome.g. electrically conductive wires, ribbon, or flex circuit material.

FIG. 3A shows a diamond shaped motor coil unit 300, in accordance withthe invention. A pair of adjacent legs 302A and 302B define section 302,and another pair of adjacent legs 304A and 304B define section 304.Between sections 302 and 304 are shoulders 325. Sections 302 and 304 andshoulders 325 are integrally formed with one electrically conductivewire or ribbon of substantially uniform cross-section. Shoulders 325 arecreated along the extension line of inner borders of legs 302A and 302Bof coil unit 300. The inner borders of legs 302A, 302B, 304A, and 304Bdefine a diamond shaped closed conductive band surrounding a diamondshaped void in the central portion.

Sections 302 and 304 are arranged in a step-like relationship, wherebysection 302 resides in a first plane and section 304 resides in a secondplane parallel to and offset from the first plane. The distance betweenthe first and the second planes varies depending on the cross-section ofthe wire and number of layers. When the coil unit has only one layer ofwire, the distance between the first and the second planes isapproximately equal to the thickness of the wire. A cross-sectional viewof a tip area (where adjacent legs join) formed by the legs 302B and304B of a “race track” type coil unit is shown in FIG. 3B. FIG. 3C is aview long line 3C-3C of FIG. 3B. Such a coil unit comprises a singlelayer of wire or ribbon wound continuously to form a wire band.

One step in manufacturing a race track type coil unit is to wind asuitable electrically conductive wire or ribbon with surface insulationinto a wire band. FIG. 4A shows an apparatus 407 suitable for windingthe wire band. Apparatus 407 has a flat platform 405 with four pegs 401,409, 411, and 413 installed at four positions forming the corners of adiamond shape. To wind a wire band 480, electrically conductive wire 419is wound around pegs 401, 409, 411, and 413, and back to peg 401. Theabove process repeats until a desired width is reached. During thewinding process, wire 419 is pressed closely against plate 405 to ensurethat the wire is tightly wound. Wires are carefully laid next to eachother in a planar configuration.

In some embodiments, as shown in FIG. 4A, an optional guide plate 418 isused to assist the winding of wire band 480. Guide plate 418 has fourholes 401A, 409A, 411A, and 413A in alignment with pegs 401, 409, 411and 413 on platform 405. When guide plate 418 is used, each of the pegs401, 409, 411 and 413 fits into its corresponding hole. Guide plate 418is spaced above parallel to platform 405 at a distance substantiallyequal to the thickness of the wire. A flat gap is thus formed betweenplatform 405 and guide plate 418. During wire winding, tension isapplied to the wire to ensure that wire band 480 is tight. The use ofguide plate 418 prevents the wire from slipping.

Another step in the manufacturing of a coil unit is to press flat wireband 480 into a final shape of a coil unit. This step is performed on anarbor press with a special tool. One example of a special tool 440 isshown in FIG. 4B. Special tool 440 has upper piece 442 and lower piece444. The working surfaces of both the upper and lower pieces areprofiled so that a coil unit with a desired step-like shape is produced.For example, upper piece 442 has section 446 on one side and section 448on the other side. Both sections 446 and 448 have a flat workingsurface, with the working surface of section 446 protruding beyond theworking surface of section 448. Lower piece 444 has section 454 incorrespondence with section 448, and section 464 in correspondence withsection 446. The working surface of section 454 protrudes beyond theworking surface of section 464. The working surfaces of sections 454 and464 are separated by a chevron shaped shoulder 490. Sections 448 and 446are also separated by a shoulder with a corresponding chevron shape (notshown). At a closed position a step-like air gap is formed between upperpiece 442 and lower piece 444.

During the pressing operation, wire band 480 is placed on the workingsurface of lower piece 444. Wire band 480 is so positioned that theinner borders of two adjoining legs are placed on section 454 of thelower piece 444 of tool 440 parallel and adjacent shoulder 490. Upperand lower pieces 442, 444 of tool 440 then close to grip wire band 480.Wire band 480 is thus forced to assume the shape of the air gap definedby the upper and lower pieces of tool 440. The product of the pressingoperation is a step-like coil unit 496 as shown in FIG. 4C.

Referring to FIG. 3A, coil unit 300 is of an electrically conductivewire or ribbon coated with an electrically insulating layer, e.g.insulated copper wire. Wires of other electrically conductive material,such as aluminum, silver and gold, are also suitable. Suitable copperwire is available from MWS, Los Angeles, Calif. In one example, the wireused is American Wire Gage (AWG) 19 heavy build copper wire (ofapproximately 1.0 mm diameter.) In another example, the wire used is AWG16 heavy build copper wire (of approximately 1.3 mm diameter.) Thefinished coil is assembled in a “can” (housing) of e.g. magneticallyimpermeable 300 series stainless steel, preferably 304 stainless steel.In some embodiments other magnetically impermeable materials such asaluminum, or ceramic are used for the can. Similar materials are usedfor making coils of other configurations described in thisspecification.

FIGS. 5A and 5B are plan and-cross-sectional views, respectively, of onerow of motor coil units 501. In FIG. 5A, all coil units 502-507 arearranged in a staggered overlapping relationship, wherein each coil unitis partially on top of another coil unit. For example, coil unit 503 isstacked partially on top of coil unit 502, and coil unit 504 is stackedpartially on top of coil unit 503. With this arrangement, for each rowof coil units the working area, other than a small portion around theperimeter of the working area, has a thickness of two layers of coilunits. Because of the substantial uniformity in thickness, a linearmotor coil manufactured according to the embodiment has a flat head areaand is easy to install and remove in the track. A final motor coilnormally uses several rows of coil units such as the one shown in FIGS.5A and 5B stacked with their respective working areas directly on top ofeach other.

A linear motor in some embodiments has a moving coil configuration; inother embodiments a linear motor has a moving magnet configuration. In amoving magnet configuration, the motor coil is fastened to a part of adevice, such as a base of a stepper (x-y) stage, and the magnetic track(fastened to the stage) moves relative to the coil. The coil is maderelatively long, about the range of travel of the motor plus the lengthof the magnetic track. On the other hand, the magnetic track is maderelatively short, only long enough to hold magnets for generatingsufficient Lorentz force to propel the moving part of the motor.

In a moving coil configuration, the magnetic track is fastened to thebase of the movable device and the coil (fastened to the stage) movesrelative to the magnetic track. The magnetic track is made to berelatively long, about the range of travel of the linear motor plus thelength of the coil. On the other hand, the coil is made relativelyshort.

The row of motor coil units 501 shown in FIGS. 5A and 5B is suitable fora moving coil motor. By adding more coil units, row of coil units 501 isthereby lengthened and made suitable for use in a moving magnet motor.Illustratively, the relevant dimensions of a row of coil units 501 shownin FIGS. 5A and 5B, are listed in Table 1:

TABLE 1 Relevant dimensions of a row of coil units, as shown in FIGS. 5Aand 5B. Dimension Length (mm) D51 1 D52 2 D53 104 D54 6.95 D55 50 D5633.32 D57 24.99 D58 16.66 D59 8.33 D510 8.33

Another example of a motor coil according to the invention is shown inFIGS. 6A (plan view) and 6B (cross-sectional view). Coil unit 601 inFIGS. 6A and 6B is called a folded tip coil unit because of its twofolded tips 602 and 603. Each of folded tips 602 and 603 has a foldradius such as fold radii 607 and 609. Fold radii 607 and 609 are oftendesirable for protecting the surface insulation of the coil wire and forpreventing the wire from breaking.

FIGS. 7A (plan view) and 7B (side view) show several folded tip coilunits assembled together to form a row of motor coil units 701. Similarto row of motor coil units 501 shown in FIG. 5A, row of motor coil units701 has two layers of wire across the majority of its working area,while along a small portion at the ends of row 701 there is one layer ofwire. Illustratively, shown in FIGS. 7A and 7B are the relevantdimensions listed in Table 2 for a row of folded tip diamond shapedlinear motor coil units 701.

TABLE 2 Relevant dimensions for a row of folded tip diamond shapedlinear motor coil units, as shown in FIGS. 7A and 7B. Dimension Length(mm) D71 1 D72 2 D73 104 D74 50 D75 33.32 D76 24.99 D77 16.66 D78 8.33D79 8.33

One step in making such a folded tip diamond shaped coil unit is to windan electrically conductive wire into a wire band. An apparatus forwinding a folded tip diamond shaped wire band is shown in FIG. 8A. Theapparatus includes a first thin plate 805 and a second thin plate 804held apart by removable braces 831 and 832. The width of the apparatusis defined by edge 819 of thin plate 805 and edge 829 of thin plate 804.A blade 810 extends symmetrically perpendicular to the plane of thinplate 805. Blade 810 of thin plate 805 coincides with the center line ofthe apparatus as shown in FIG. 8A and contains a row of guide teeth 809on each edge. Guide teeth 809 are arranged in a comb-like fashion andare perpendicular to the plane of thin plate 805.

To wind a diamond shaped folded tip wire band, wire 807 is wound aroundpoints A, B, C, and D, where it is held in fixed positions at points Band D by two pairs of guide teeth. Wire 807 is then wound to positionA′, where the winding process is repeated until the wire band hasreached a sufficient width. Removable braces 831 and 832 are thenremoved to allow thin plates 805 and 804 to be separated from the wireband.

FIG. 8B shows another apparatus for winding a wire band. The apparatusincludes a thin plate 881 and three chevron shaped pieces 891, 882(shown cutaway), and 885. The process for winding a wire band using thisapparatus starts with placing thin plate 881 between chevron shapedpieces 891, 882, and 885. Wire 883 is started at the near end of achevron surface 878 of chevron shaped piece 885 and is wound along theintersection between chevron surface 878 and thin plate 881. At the farend of surface 878, wire 883 passes around thin plate 881 to follow achevron surface 880 of chevron shaped piece 882, where it is held inplace by a spacer (not shown) wedged between wire 883 and a chevronsurface 879 of chevron shaped piece 891. Wire 883 is wound around againsimilarly. Each time wire 883 is wound, the spacer is replaced by aslightly thinner spacer, until the gap between chevron surfaces 879 and880 is filled with wire. Chevron shaped piece 882 is needed, becausewire 883 winds from the outer border in toward the inner border in onesection of the wire band. In other embodiments, variations of this toolare applied, without departing from the inventive principle describedherein.

Another step in making a folded tip diamond shaped coil unit is to pressthe wire band into the final shape of a coil unit. This is performed onan arbor press using a press tool. FIG. 8C shows one example of such apress tool 800 having upper piece 820 and lower piece 822. Upper piece820 has a flat working surface between edges 824, 826 while lower piece822 has elevated rectangular section 823. Elevated rectangular section823 also has a flat working surface. Wire band 870 is carefullypositioned on top of the lower piece such that the body of wire band 870rests on convex section 823 while the tips extend beyond convex section823. Upper piece 820 is then lowered pressing wire band 870. Edges 824,826 control the coil unit width when it is pressed. The final shape ofthe coil unit 871 is shown in FIG. 8D.

Alternatively, the row of coil units is first stacked, then pressedtogether.

In some embodiments flex circuit coil units are used in the motor coil.Illustratively, a flex circuit coil unit is shown in FIG. 9A. Flexcircuit conventionally is a sheet of electrically conductive materialbonded with a layer of electrically insulating material 965 (see FIG.9B) such as polyimide film. FIG. 9A schematically shows two coil legs905 and 907 etched on flex circuit. In an installed position, strippedend 913 of leg 905 is electrically connected with stripped end 909 ofleg 907. Connection is made by soldering or other suitable methods.Stripped end 917 of leg 905 and stripped end 915 of leg 907 are fittedto be connected to power supply wires or to another coil unit.

FIG. 9B shows a section of. a motor coil 999 using flex circuit inaccordance with the invention. Coil legs 921, 922, 923, 924, 925, and926 are etched on one sheet of flex circuit material, while legs 931,932, 933, 934, 935, and 936 are etched on another sheet of flex circuit.The techniques for etching a flex circuit are well known to thoseskilled in the motor art.

FIGS. 9C, 9D, and 9E depict linear motors using diamond shaped coilunits. The coil unit width and wire band width relative to the magneticpitch are as shown. These examples pertain to all diamond shaped coilunits, including the race track type, folded tip type, and the flexcircuit type. Each of the examples shown has a different wire band widthrelative to the pole pitch. The motors shown in FIGS. 9C, 9D, and 9E alluse three-phase commutation. According to the invention, a linear motoris conventionally commutated using two or more phases of electriccurrent to generate long range continuous motion. Single phasecommutation is also possible, if short range linear motion is preferred.

In FIG. 9C, the width Wcl of a coil unit is equal to the magnetic pitchP1. The width Vv1 of the diamond shaped void is equal to four times thewidth of the wire band Vb1. In the example shown in FIG. 9D, the widthWc2 of the coil unit is equal to ⅔ the magnetic pitch P2. The width Vv2of the diamond shaped void is equal to twice the width Vb2 of the wireband. In the example shown in FIG. 9E, the width Vc3 of the coil unit isequal to one half of the magnetic pitch P3, and the width of the diamondshaped void Vv3 is equal to the width Vb3 of the wire band. Otherconfigurations are possible according to the invention. In analternative configuration not shown, it is desirable that the width ofthe diamond shaped void is an integral multiple of the width of the wireband.

In some embodiments a linear motor employs a hexagonal coil unit. FIG.10A shows one example of a hexagonal coil unit. A hexagonal coil unithas two straight parallel legs 1011 and 1013 that are perpendicular tothe movement direction of the coil. At the ends of the coils there aretwo triangular sections 1015 and 1017, each with two slant legsintegrally formed with straight legs 1011 and 1013. The straight legs1011 and 1013 and the triangular sections define a hexagonal shaped voidin the central portion. Because straight legs 1011 and 1013 of thehexagonal coil unit are perpendicular to the movement direction of thecoil, a greater Lorentz force is created for a given electric current incomparison with the diamond shaped coil units. Because the resistance isapproximately the same, the motor constant is higher. Theoretically, theLorentz force generated by a hexagonal coil unit is in the range ofapproximately 30% greater than that generated by a diamond shaped coilunit.

FIG. 10B is a schematic view of a linear motor having one row ofhexagonal coil units. In some embodiments a final motor coil assemblycontains one row of coil units; in other embodiments a final motor coilassembly contains a plurality of rows of coil units. When more than onerow of coil units is used, the rows of coil units are stacked on top ofeach other. One possible position of the magnets of the motor are shownin dashed lines. With a single layer coil unit, the row of coil unitsshown in FIG. 10B has two wire thicknesses across most of the workingarea. Only a small portion at the ends has one layer of wire.

In the example shown in FIG. 10B, the width Wc4 of the coil unit isequal to ⅔ of the magnetic pitch P4. The hexagonally shaped void has awidth Vv4 of twice the width Vb4 of the wire band. In another example ofa linear motor shown schematically in FIG. 10C, the width Wc5 of thecoil unit is equal to one half of the magnetic pitch P5. The width ofthe hexagonal shaped void Vv5 is equal to the width Vb5 of the wireband. Other alternative configurations are possible according to theinvention. In each of these configurations, it is desirable for thewidth of the hexagonal shaped void to equal an integral multiple of thewidth of the wire band.

Both race track type and folded tip type hexagonal coil units aremanufactured according to the invention. One step in making a race trackhexagonal coil unit is to wind a flat wire band. This is performed usingan apparatus similar to that shown in FIG. 4A. Since a coil unit in thisexample has a hexagonal shape, the apparatus shown in FIG. 4A must bemodified to have 6 pegs instead of 4 pegs. Another step in making a racetrack hexagonal coil unit is to press the wire band into the final shapeusing a press tool similar to that shown in FIG. 4B.

A variation of the coil unit shown in FIG. 10A is the folded tiphexagonal coil unit 1100 as shown in FIGS. 11A (plan view), 11B (sideview), and 11C (perspective view). Coil unit 1100 is called a folded tiphexagonal coil unit because of the folded tips 1102 and 1104. Coil units1100 has two sections 1108 and 1110. Section 1108 is in a first plane,while section 1110 is in a second plane parallel and offset from thefirst plane. The first and second planes are set apart by apredetermined distance. The distance between the first plane and thesecond plane varies to maximize conductor density, and is typically onewire thickness for a single layer coil unit.

One step in making folded tip coil unit 1100 is to wind a hexagonal wireband. An apparatus for winding a wire band is shown in FIG. 12. Thisapparatus is similar to that shown in FIG. 8A, but with two rows ofguide teeth 1209 on each of plates 1205 and 1206. Plates 1205 and 1206are stretched apart by removable braces 1201. To wind a wire band usingthe apparatus shown in FIG. 12, wire 1207 is first wound around pointsA, B, C, D, E, and F. At each of points B, C, E, and F, wire 1207 isheld in a fixed position by a pair of guide teeth. The wire then iswound around point A′ and the process repeats until a design width isreached. Removable braces 1201 are then removed to allow plates 1205 and1206 to be separated from the wire band. In a subsequent step, the wireband is pressed into the final shape of a coil unit in an apparatussimilar to that shown in FIG. 8B.

FIGS. 13A (plan view) and 13B (side view) show a linear motor coil usingfolded tip hexagonal coil units, according to the invention. The coilunits are installed in a staggered overlapping configuration to form acoil with a substantially uniform thickness. The coil units areinstalled in a can of non-magnetic material, e.g., 300 series stainlesssteel (or aluminum, ceramic, etc.).

One problem in designing a wire band for making a hexagonal coil unit,either a race track type or a folded tip type, is the wire band width.FIG. 14 shows a position of a wire band according to the invention thatexemplifies the problem. In FIG. 14, the wire band has a width W.Slanted legs 1401 and 1402 of the coils are stacked closely against eachother in order to maximize conductor density. At the parallel legsection, however, the distance between the edges of two neighboring legsis W1. If the angle between the slant leg and the straight leg is Ø, thedistance W1 between the two neighboring parallel leg edges is W dividedby cos Ø:

W 1=W/cos Ø.

Since cos Ø is less than 1, W1 is always larger than W. The larger theangle Ø, the larger the distance W1.

Because the distance between the neighboring leg edges is larger thanthe width of a leg, special winding techniques must be used to assurethat a uniform coil thickness is obtained. One arrangement is to usetight wound coil units illustrated in FIG. 14. In FIG. 14, a coil unitis tightly wound so that no space is left between neighboring sectionsof a wire. The width of the straight leg and that of the slant leg areboth equal to W. When the coil units are assembled to form a coil,however, a small gap appears between adjacent straight legs. The widthof the gap is W1−W.

Another arrangement is to use the loose wound coil units shown partiallyin FIG. 15. The extra width W1−W in this type of coil unit isdistributed among the neighboring wire sections within the same coilunit. In FIG. 15, each slant leg has a width W, while each straight leghas a width of W1. Each wire section in the slant leg is packed tightlynext to the other. In the straight leg section each wire is spaced apartfrom each other. The width of the gap Wg between one wire section and aneighboring wire section is expressed in the following formula:

Wg=(W 1−W)/(n−1),

where n is the number of wires wound in a wire band. In someembodiments, the above described winding arrangements are used for boththe race track type and folded tip type hexagonal coil units.

Referring to FIGS. 11A, 11B, 13A, and 13B, the relevant dimensions ofthree examples of a motor coil are given in Table 3. Although the motorcoil shown in FIG. 13A is a moving coil, a moving magnet motor coil isproduced by adding more coil units to the assembly, as shown by thedimensions for one example of a moving magnet motor in Example 3 ofTable 3. Illustratively, the length D1112 for the moving magnet motorcoil of Example 3 is much larger than for the moving coils of Examples 1and 2, because there are a larger number of coil units in each row ofExample 3.

Table 3. Relevant coil dimensions for three examples of a motor coilshown in FIGS. 11A, 11B, 13A, and 13B. Dimensions are in millimetersunless otherwise specified.

Example 1, Example 2, Example No., Loose Wound Tight Wound Example 3,Motor Type Moving Coil Moving Coil Moving Magnet Number of 6 6 33 CoilUnits in a Row D1101 1.0 1.0 1.0 D1102 2.0 2.0 2.0 D1103 104 104 104D1104 87.2 87.2 87.2 D1105 16.67 17.55 17.55 D1106 8.33 7.45 7.45 D11077.45 7.45 7.45 D1108 33.33 32.45 32.45 D1110 26.6 26.6 26.6 (degrees)D1112 74.97 74.09 299 coil length D1113 24.99 24.99 24.99 D1114 16.6616.66 16.66 D1115 8.33 8.33 8.33

Another example of a linear motor according to the invention uses a flexcircuit for making a motor coil unit. FIG. 16A shows a row of coil legsfor making hexagonal coil units. Partition gaps 1602 are etched on theconductor layer of the flex circuit, leaving coil unit legs 1601mutually insulated from each other. Flex circuit coils avoid thedifficulties associated with band width as described above in connectionwith FIGS. 14 and 15, because the insulating gaps are etched onto asingle substrate instead of being wound.

The conductor layer on a sheet of flex circuit commonly has a smallthickness, in the range of a fraction of a millimeter. Thus multiplelayers are normally used in a motor coil to generate sufficient Lorentzforce. FIG. 16B schematically illustrates the inter-layer electricalconnection of a section of coil legs. At coil leg head area 1611A, theinsulation layer is shown etched away to expose the conductor layer, andthe conductor layer is electrically connected to an outside power supplycable or to a neighboring coil unit through an interconnect (such asinterconnect 1650 in FIG. 16D). One end of the coil has no insulation oneither side; the other end has insulation on one side.

Head area 1611B of leg 1611 is electrically connected to head area 1621Bof leg 1621, in which area the insulation layer is similarly etchedaway. Head area 1621A of leg 1621 is electrically connected to head area1612A of leg 1612. The other coil leg heads are connected in a similarfashion. In a motor coil connected using this configuration, electriccurrent flows in a spiral fashion from one leg to another leg in thedirection indicated by the arrows. The electrical connection is madewith solder or other electrically conductive adhesive material, such aselectrically conductive epoxy or pressure sensitive tape. In someembodiments, other electrical contacting materials are used. At the lastcoil leg 1623, the head area 1623A is electrically connected to anothercoil or to a power supply cable.

FIG. 16C illustrates a cross section of a motor coil where the areas formaking the electrical connection are enlarged to show details.Insulation layer 1661 of e.g. polyimide film and conductor layer 1671 ofe.g. copper form a first sheet of flex circuit. Insulation layer 1662and conductor layer 1672 form a second sheet of flex circuit. The othersheets of flex circuits are similar in structure. An extra insulationlayer 1668 is provided at the bottom to insulate to the last conductorlayer.

Conductor layer 1671 is etched to form a row of coil legs analogous to,for example, leg 1611 of FIG. 16B. Conductor layer 1672 is etched toform a row of coil legs analogous to, for example, leg 1621 of FIG. 16B.At end 1699 and between lines 1693 and 1694, the insulation layer 1662is etched away to expose conductor layer 1672, to form a leg head areaanalogous to, for example, head area 1621B of FIG. 16B. Electricalconnection is established using electrically conductive material 1681.At end 1698 and between lines 1691 and 1692, insulation layer 1663 isetched away to expose conductor layer 1673. Electrical connectionbetween conductor layers 1672 and 1673 is established using electricallyconductive material 1682. Insulation layer 1661 is etched away at end1698 to expose conductor layer 1671 to form an area 1675, which isanalogous to, for example, area 1611A of FIG. 16B. A similar exposedarea 1674 is etched on insulation layer 1668 at the opposite side.

FIG. 16D shows a motor coil core after the electrical connection hasbeen established. A series of interconnects, such as interconnect 1650,electrically connects one coil unit to another coil unit of the samephase group.

Yet another configuration of a motor coil according to the inventionuses double diamond shaped motor coil units as shown in FIG. 17A. Coilunit 1700 has two cross legs C′E and BF intercepting each other at pointO. Point O thus divides leg C′E into two equal length sections C′O andEO and divides leg BF into two equal length sections BO and FO. SectionsBO and EO and legs AE and AB form one diamond shape, and sections FO andC′O and legs D′F and C′D′ form another diamond shape.

One step in making a double diamond shaped coil unit is to wind aparallelogram wire band. In some embodiments the parallelogram wire bandis a race track type. In some embodiments the parallelogram wire band isa folded tip type. A race track type parallelogram wire band ABDC isshown in FIG. 17A, partially in dashed lines. Parallelogram wire bandABDC is wound so that the length of the two long legs AC and BD is threetimes the length of the two short legs AB and CD. When parallelogramwire band ABDC is folded at points E and F into a double diamond shapedcoil unit 1700 (all solid lines), points C and D become points C′ and D′respectively, and legs BF and EC′ intersect at point O. In someembodiments a race track type parallelogram wire band is wound using anapparatus similar to that shown in FIG. 4A, as described above.

FIG. 17B shows a folded tip type parallelogram wire band A₁B₁D₁C₁(partially in dashed lines) having folded tips B₁ and C₁. Whenparallelogram wire band A₁B₁D₁C₁ is folded at points E₁ and F₁ into adouble diamond shaped coil unit 1702 (all solid lines), points C₁ and D₁become points C₁′ and D₁′ respectively, and legs B₁F₁ and E₁C₁′intersect at point O₁. In some embodiments an apparatus similar to thatshown in either FIG. 8A or FIG. 8B is employed to wind a folded tipparallelogram wire band.

Subsequent to the winding of a wire band, another step in making thedouble diamond shaped coil unit is to stack a desired number of wirebands in a shingle like relationship. FIG. 18 shows five wire bands1801, 1802, 1803, 1804, and 1805 stacked together. Since the stackingprocesses for a race track type and a folded tip type wire bands aresimilar, FIG. 18 is used to illustrate both types, even though racetrack type wire bands are shown. Wire band 1804 is stacked partially ontop of wire band 1805, and the outside edges of legs 1804C and 1804D areclosely against the inside edges of the corresponding legs 1805C and1805D of wire band 1805. Similarly wire band 1803 is stacked partiallyon top of wire band 1804, and the outside edges of legs 1803C and 1803Dare closely against the inside edges of the corresponding legs 1804C and1804D. In a similar fashion, wire bands 1802 and 1801 are stacked on.Pressure sensitive tape or an adhesive hold the wire bands together.

Another step in making a motor coil is to fold the stacked parallelogramwire band into a motor coil unit. In FIG. 18, two fold points E and Fare chosen for wire band 1801. Fold point E is chosen so that the lengthof CE is twice the length of AE. Similarly, fold point F is chosen sothat the length BF is twice the length FD. Folding points are chosen oneach of the wire bands. Because of the uniformity of wire band shape andsize, the fold points form a straight line.

FIG. 19 shows a row of double diamond shaped coil units 1900 formed ofwire bands after the folding process. Rows of linear motor coil unitsusing folded tip wire bands are similar. In some embodiments these rowsof coil units are stacked, shingle-like to form longer coils.

In accordance with the invention, it is also possible to make a doublediamond shaped coil unit using flex circuit, with the coil wiresinsulated on both sides.

In some embodiments the rows of motor coil units of any shape describedabove are used in a single row motor coil configuration. In someembodiments the rows of motor coil units of any shape described aboveare used in a multi-row motor coil configuration.

FIG. 20A shows a magnetic track 2000 for a moving magnet linear motoraccording to the invention. Magnetic track 2000 includes rail 2005 andtwo side rails 2006 attached to rail 2005 by screws 2001 to form a “U”shape. Magnets 2003 and short magnets 2004 are attached to side rails2006 to form magnet pairs. Magnets of each pair face each other across agap.

Rail 2005 is of non-magnetic material, such as 304 stainless steel,aluminum or ceramic. Side rails 2006 are of magnetic material (e.g.steel) with saturation flux density equal to or greater than 16,000gauss. Magnets 2003 and short magnets 2004 are of e.g. high qualityNdFeB permanent magnet material with a permanent magnetic flux densityof 13,500 or greater gauss. A higher motor constant is obtained if themagnetic flux density is higher. The magnets are coated to preventcorrosion.

FIG. 20B shows the arrangement of the magnetic flux path of the magnetictrack shown in FIG. 20A. By properly arranging the polarity of themagnets, the magnetic flux across the magnetic track forms closed loops.

FIG. 21 shows a magnetic track 2100 for a moving coil motor according tothe invention. Magnetic track 2100 includes rail 2105 and two side rails2106 attached to rail 2105 by screws 2101 to form a “U” shape. Magnets2103 and short magnets 2104 are attached to side rails 2106 to formpairs of magnets. Magnets of each pair face each other across a gap.Illustratively, magnetic track 2100 is made of the same materials asmagnetic track 2000 in FIG. 20A. As described above, magnetic track 2100for a moving coil motor is longer than magnetic track 2000 for a movingmagnet motor.

Although the present invention is described in terms of severalembodiments, these embodiments are illustrative only and do not limitthe scope of the invention. Numerous modifications can be made withoutdeviating from the spirit of the invention. For example, although thecoil units in the described embodiments contain one layer of wire, coilunits in other embodiments contain two or more layers of wire. In someembodiments a coil unit with two layers of wire is formed by stackingone single layer coil unit on top of another single layer coil unit.These and other variations fall within the scope of the invention, whichis best defined by the following claims.

What is claimed is:
 1. A linear motor coil, operable in cooperation withan associated magnet track, comprising: a plurality of coil units, eachsaid coil unit configured into a geometric polygonal shape defining asubstantially planar band surrounding a void, and wherein said pluralityof coil units are arranged linearly, and wherein each said coil unitcomprises a first sheet and a second sheet of laminar material, eachsaid sheet including a plurality of substantially coplanar electricallyconductive members bonded to a substantially planar electricallyinsulating substrate, at least one said conductive member of said firstsheet being joined to at least one said conductive member of said secondsheet.
 2. A linear motor comprising: a magnet track; and a motor coiloperating in cooperation with said magnet track and having a pluralityof coil units, each said coil unit configured into a geometric polygonalshape defining a substantially planar band surrounding a void, andwherein said plurality of coil units are arranged linearly wherein eachsaid coil unit comprises a first sheet and a second sheet of laminarmaterial, each said sheet including a plurality of substantiallycoplanar electrically conductive members bonded to a substantiallyplanar electrically insulating substrate, at least one said conductivemember of said first sheet being joined to at least one said conductivemember of said second sheet.
 3. An electric motor comprising: at leastone magnet; and a motor coil operating in cooperation with said at leastone magnet and having at least one coil unit comprising a first sheetand a second sheet of laminar material, and each said sheet including aplurality of substantially coplanar electrically conductive membersbonded to a substantially planar electrically insulating substrate, atleast one said conductive member of said first sheet being joined to atleast one said conductive member of said second sheet.
 4. An electricmotor according to claim 3, wherein said motor coil is a linear motorcoil, and wherein said at least one magnet is configured as a linearmagnet track.
 5. An electric motor according to claim 3, wherein saidmotor coil has a plurality of coil units, each said coil unit beingconfigured into a geometric polygonal shape defining a substantiallyplanar band surrounding a void, wherein said void has a width which isan integral multiple of a width of said substantially planar band.
 6. Alinear motor according to claim 5, wherein said geometric polygonalshape is a diamond shape.
 7. A linear motor according to claim 5,wherein said geometric polygonal shape is a hexagonal shape.
 8. A motorcoil operable in cooperation with an associated magnet track,comprising: a plurality of coil units, each said coil unit configuredinto a geometric polygonal shape defining a substantially planar bandsurrounding a void, wherein each said coil unit comprises a plurality ofsheets of laminar material layered on each other, each said sheetincluding a plurality of substantially coplanar electrically conductivemembers bonded to a substantially planar electrically insulating memberand wherein said plurality of coil units are arranged linearlysubstantially along the direction of a driving force of the linearmotor.
 9. A motor coil according to 8, wherein said plurality of coilunits are arranged such that at least one coil unit partially overliesand adjacent coil unit to form at least one row of said coil units, saidat least one row being substantially parallel with the direction of thedriving force of the motor coil and magnet track.
 10. A linear motorcomprising: a magnet track; and a motor coil operating in cooperationwith said magnet track and having a plurality of coil units, each saidcoil unit configured into geometric polygonal shape defining asubstantially planar band surrounding a void, wherein each said coilunit comprises a plurality of sheets of laminar material layered on eachother, each said sheet including a plurality of substantially coplanareletrically conductive members bonded to a substantially planarelectrically insulating member, and wherein said plurality of coil unitsare arranged linearly substantially along the direction of a drivingforce of the linear motor.
 11. A linear motor according to claim 10,wherein said plurality of coil units are arranged such that at least onecoil unit partially overlies an adjacent coil unit to form at least onerow of said coil units, said at least one row being substantiallyparallel with the direction of the driving force of the linear motor.